A thin-film electron source has three-thin-layer structure, such as an upper electrode-an insulating layer-a lower electrode, and it emits electron into a vacuum from the surface of the upper electrode, by applying voltage between the upper electrode and the lower electrode, having such a polarity that the upper electrode comes to have a positive one. The operation principle of the thin-film electron source is shown in FIG. 2. A driving voltage 20 is applied across the upper electrode 13 and the lower electrode 11, so as to establish the electric field of around 10 MV/cm within the insulating layer, then electron in the vicinity of the Fermi level within the lower electrode 11 penetrates through the barrier due to the Tunnel phenomenon of Fower-Nordheim, so as to be injected into conductive bands of the insulating layer 12 and the upper electrode 13, thereby becoming hot electrons. Among those electrons, those having energy being equal to or greater than the work function .phi. of the upper electrode are emitted into the vacuum 16. Because of utilization of the Tunnel phenomenon, the film thickness of the insulating layer must be very thin, such as being about from 3 nm to 15 nm.
With such the thin-film electron source, it is possible to generate electron beam from any place where a matrix is formed by crossing or intersecting plural pieces of the upper electrodes and plural pieces of the lower electrodes, therefore it can be used as an electron source in a display device, or the like.
Heretofore, emission of electron was observed from MIM (Metal-Insulator-Metal) structure, such as Al--Al.sub.2 O.sub.3 --Au structure.
In particular, with the thin-film electron source, which uses Al as the lower electrode and anodized film (or film oxidized by anodic oxidization) as the insulating layer, since it is possible to form Al.sub.2 O.sub.3 insulating layer, being durable with high voltage and having a uniform thickness due to the anodic oxidization or anodization as well, then the electron emission of good quality can be obtained.